Prior art slide calculators have been provided for calculating proper refrigerant charge for refrigeration systems, such as for use in servicing building air conditioning systems for heating and cooling. Typically, the pressure and temperature of the refrigerant at one point in the refrigeration system is measured, and then compared to desired refrigeration performance characteristics to determine whether there is a proper amount of refrigerant within the system. The prior art slide calculators have been used to translate the measured temperature and pressure for comparison in relation to the performance characteristics. However, prior art slide calculators provide data in tabular format that is data tables, rather than graphical representations in which positions in linear and logarithmic scales represent various changes in temperatures and pressures according to corresponding performance characteristics and measured pressures and temperatures. Recently, due to environmental concerns, refrigerants such as R22 have been replaced with new refrigerants such as R410a which are perceived as less harmful to the environment. The older refrigerants utilize hydro fluorocarbons and newer refrigerants utilize difluoromethane. This has resulted in prior art refrigerant charge slide calculators being required for each type of refrigerant being used. This is cumbersome with service technicians often required to carry numerous refrigerant charge slide calculators, at least one per type of refrigerant used. Since prior art slide calculators use tabular forms rather than graphical representations, it is not practical to provide prior art slide calculators with tabular representations in which more than one type of refrigerant is displayed for a refrigerant charge slide calculator.